Hot working of materials



Aug. 15, 1967 J. BUFFET HOT WORKING OF MATERIALS 2 Sheets-Sheet 1Original Filed Oct. 29, 1964 lll'l-llll llllll I 'll HOT WORKING OFMATERIALS Original Filed Oct. 29, 1964 2 Sheets-Sheet 2 INVENTOR. JEA/VBUFFET United States Patent M 3,335,589 HOT WORKING OF MATERIALS JeanBuffet, Versailles, France, assignor to Compagnie du Filage des Metauxet des Joints Curty,.Paris, France Original application Oct. 29, 1964,Ser. No. 408,465, new

Patent No. 3,182,474, dated May 11, 1965. Divided and this applicationFeb. 26, 1965, Ser. No. 435,556

2 Claims. (Cl. 72-41) This is a division of application Ser. No.408,465, filed Oct. 29, 1964, now Patent No. 3,182,474.

This invention relates to methods of hot-working materials, particularlymetal and alloys, and is chiefly concerned with the hot-working forextrusion and boring or piercing materials having high resistance todeformation, especially certain metals and alloys.

The invention is broadly applicable to the hot-working for extrusion andboring or piercing such materials, including especially high-speedsteels, refractory alloys, allied steels, alloys comprising a number ofphases and the compositions known as cermets and the like. Extremediffi-culties have often been experience in the past when exposing suchmaterials to hot-working processes such as extrusion, piercing, and thelike, because of the deformation of cracks and similar flaws at thesurface of the material during the hot-working process. A chief factorresponsible for this cracking tendency has been the sudden coolingeffect exerted on the surface of the heated ingot or billet by the coolsurfaces of the hot-working press equipment that act thereon. Since thematerials under consideration are, as a general rule, poor heatconductors, such heat is not transferred to the core of the billetrapidly enough to avert the setting up of steep thermal gradients in thematerial, which in turn generate high internal stresses resulting in theaforementioned cracks.

In Buffet and Meriaux prior patent application No. 646,192 of Mar. 15,1967, now abandoned for Method of Hot Extrusion of Metals, an improvedmethod of hotworking brittle materials wasdisclosed, wherein the ingotor billet of material was encased in a readily deformable metallic caseor sheath. While this prior method has constituted a noteworthy advancein the art and has permitted the hot-working of metals and othermaterials which were not practically amenable to such treatment in thepast, it had certain disadvantages which it is the specific object ofthe present invention to eliminate.

The chief drawback of the earlier method just recalled (the method ofapplication 646,192) was the fact that the hot-worked, e.g. extruded orotherwise deformed, article obtained was itself coated with a thincoating of foreign material constituted by the sheath or case deformedsimultaneously with the material. The removal of i this coating, bymechanical or chemical means, constituted a supplementary operationwhich complicated the process. Moreover, the final hot-worked articleafter removal of the coating was in certain cases apt to exhibit surfaceflaws or roughness. Also dimensional accuracy was difficult to maintainin view of the variations in thickness of the deformed case.

A broad object of this invention is to provide an improved method ofhot-working of such materials which are difficult to be deformedheretofore even by hot-working. Another obpject is to provide such amethod in which the final hot-worked article will be produced in adirectly usable form.

The invention provides a method of hot-working, which comprises encasinga billet or ingot of the material in a case or sheath having somewhatlarger inner dimensions than the outer dimensions of the billet todefine clearance space therewith, interposing in said space a mass oflub- 3,335,589 Patented Aug. 15, 1967 ricant substance so selected as tohave substantial viscosity in the range of desired hot-workingtemperatures, heating the billet, and case to said desired range,placing the heated cased billet into a press chamber having wallsurfaces closely surrounding the case, and applying hotworking pressureto the billet but not the case in the chamber so as to form a hot-workedarticle from said billet, which article slides along the major portionof the case or sheath during deformation, While said case or sheathremains in position in the press chamber without being substantiallydeformed.

Owing to the presence of the heated sheath encasing the material, thelatter will be effectively protected from rapid cooling from thehot-working tooling equipment acting thereon, and will therefore nottend to develop cracks or other defects but will deform smoothly anduniformly throughout. Furthermore, the provision of a layer of viscouslubricant material (e.g. glass) between the material and its case willenable the material to'be readily separated from the case on, or after,being subjected to the desired hot-working step. Thus, where the methodis applied to a hot extrusion process for example, extruding pressurecan be applied only to the billet but not to the surrounding case orsheath, so that only the billet will be extruded out of the extrusionchamber through the usual die plate orifice while the case will remainin the chamber.

It will be understood that the word billet as used herein and in theclaims serves to designate any body of the material to be hot-worked,such as a cast ingot for example, in the form in which it is to besubjected to the hot-working operation.

The lubricant substance may be any substance selected so as to exhibitsubstantial viscosity in the range of temperatures to which the materialis to be exposed. Where the material is metallic, the lubricantsubstance is suitably vitreous in character, e.g. powder glass.

The billet and its case or sheath may be heated simultaneously with theformer encased in the latter, or billet and sheath may be heatedseparately and the heated billet encased in the heated sheath.

The above and further features and advantages of the invention willstand out clearly from the ensuing description, made with reference tothe accompanying diagrammatic drawings, given by way of illustration butnot of limitation, and wherein:

FIG. 1 shows in vertical section a billet encased in a sheath accordingto one form of embodiment of the invention;

FIG. 2 is a similar view relating to a modified embodiment;

FIG. 3 illustrates an encased billet of the kind shown in FIG. 1 placedin position in the extrusion chamber of a suitable extrusion press,adjacent parts of which are diagr-ammatically shown, before beginning ofthe actual extrusion process;

FIG. 4 is a view similar to FIG. 3 towards the end of the extrusionprocess;

FIG. 5 is a fragmentary vertical section view showing the billet of FIG.1 disposed in apparatus for hot piercing same; and

FIG. 6 is a View similar to FIG. 5 showing the billet of FIG. 5 duringthe piercing operation.

Referring first to FIG. 1, a billet 2 made from an alloy that isdifficult to work is surrounded by a case or sheath 1, the walls ofwhich are spaced from the surfaces of the billet so as to provide asubstantially uniform clearance space, say of about 1 mm, in width, inwhich a coat of suitable lubricant substance 3 is interposed. Thelubricant 3 may be any suitable substance having suflicient viscosity inthe working temperature range so as not to flow out during the workingprocess, and is preferably a substance of vitreous character, e.g.powdered glass. The lubricant coast or layer 3 may be provided by anysuitable method, e.g. it may be spray-coated over the surface of thebillet and/or the sheath 1.

In the modified embodiment illustrated in FIG. 2, the case or sheath 1'is open at both ends. Moreover, the billet 2 is shown as having a plugor disk 4 of some suitable inexpensive metal overlying its upper end inorder to avert losing valuable alloys at the end of the billet to beengaged by the extrusion punch or equivalent pressure means.

The composite assembly comprising the case 1 or 1', lubricant 3 andbillet 2, of either of the forms shown in FIGS. 1 and 2, is heated to asuitable extrusion temperature, and is then placed into the container '6of a conventional extrusion press, as shown in FIG. 3. Alternatively,the billet 2 and case 1 or 1 may be heated separately before assembly.In this example the extrusion press comprises a dieplate member 7positioned at the base of the container and having an extrusion orificetherein, and a plunger or punch 8 penetrating into the container fromthe upper end of it and slidable in the container. A diskshaped plug oflubricant material 5 is positioned atop the die plate 7 according tousual procedure to facilitate the initial operation. The punch 8 isfitted with a dummy block 9 having a diameter just smaller than theinner diameter of case 1.

In operation, when pressure is applied to the upper end of punch 8 withconventional press mechanism not shown, the punch end piece 9 engagesthe upper surface of billet 2 within the case 1 and forces the billetthrough the bottom wall of the case and through the die plate, as shownin FIG. 4, to provide the extruded product at 2'. The case 1 itselfremains in the container and is not forced out.

In one practical embodiment of the invention, described by way ofillustration, a billet was prepared from precipitation-hardenednickel-cobalf-molybdenu'm alloy, a material which is found to beimpossible to extrude by conventional methods without cracking. Thecomposition of this alloy was:

Percent C 0.15 Mn 0.75 Si 0.75 Cr 20 Co 13 Mo 4 Ti 3 Al 2.75 Fe 4 NiBalance The billet, 56 mm. in diameter and 80 mm. long, was spray-coatedwith powdered sheet glass over its outer surface, and was placed into amild-steel case of 57 mm. inner diameter and 60.5 mm. outer diameter.The assembly was heated in an electric furnace to a temperature of 1,050C. A die plate of 27 mm. orifice diameter was used. The inner diameterof the container was 62 mm., and the extrusion punch was fitted with anend piece 9 which was 57 mm. in diameter. A disk of sintered sheet glasspowder about 4 mm. deep was placed on top of the die plate.

The resulting extruding article was found to be entirely free of cracks.

The method of the invention was further used to hot pierce holes inalloys of the type having a general composition Ni 20%, Cr, 20%, Co,20%, balance, iron. Billets 185 mm. in diameter and 480 mm. long wereformed from this alloy, spray-coated with a suspension of powdered sheetglass, and inserted into a sheath of mild steel 187 mm. inner diameterand 207 outer diameter, and heated to a temperature of 1100 C. in anelectric furnace. The heated assembly was then placed into the containerof a vertical piercing press to have a mm. dia. hole pierced therein.The inner diameter of the container was 210 mm. The piercing press usedin this example was of the general type disclosed in the prior patentapplication of Jean Buffet and Joseph Meriaux No. 592,849 of June 21,1956 for Method of Boring Metals (now Patent No. 2,956,337).

Referring to FIGURES 5 and 6- the composite assembly of FIGURE 1comprising the case 1, lubricant 3 and billet 2 is heated without anyparticular precautions to a required piercing temperature (about 1000C.), and thereafter the assembly is placed in a container 10 of a hotpiercing press 10a. A piercing head 11 is placed at the end of a mainpiercing punch 12. The diameter of the head 11 is slightly greater thanthat of the main punch 12, and is equal to that of the bore which is tobe pierced in the billet 2.

The main punch 10 is surrounded by a secondary punch 13 the outerdiameter of which is slightly smaller than the inner diameter of case 1and the inner diameter of which is slightly greater than that of thepiercing head 11.

A pressing force is first applied to the main punch 10 and the secondarypunch 12 simultaneously so that a compression of the billet 2 resultswhereby the diameter of the case 1 slightly increases to eliminate theclearance between case 1 and container 10' while the length of the case1 remains substantially the same.

The total pressing force is then applied to the main punch 12 to effectpiercing of the billet 2 during which the upper face thereof rises up toor moves rearwardly to position 2. Also, during piercing the lubricant 3favors sliding of the billet along the inner surface of the case 1, theshape of which remains unchanged (FIGURE 6).

As previously stated the case or sheath 1 is found to exert an effectiveprotective action upon the outer surface of the billet, so that there isno sudden cooling of this surface on contact with the walls of thecontainer, die and punch member, or similar hot-working toolingcomponents. As a result, there are no steep temperature gradients set upin the material, and the latter is thus able to deform smoothly anduniformly throughout its mass without any tendency to develop cracks.

As mentioned earlier the billet 2 may first be inserted into the case 1or 1' together with the lubricant layer, and the assembly may be bodilyheated to the desired temperature, or alternatively the billet and casemay be separately heated and the heated billet inserted into the heatedcase; in this latter procedure it is found advisable to provide asomewhat larger clearance space between the surfaces of the billet andthe case, e.g. about 2 or 3 In order to ensure more positively that thecase will be retained within the container, in the deformation processesof the general types described above, it may be desirable to subject theouter surface of the case 1 to a treatment that will increase itsadhesion to the surrounding wall surfaces of the container. This may bedone by merely omitting any lubrication whatever between the case andcontainer, and/ or by oxidizing the outer surface of the case as byheating in an oxidizing atmosphere.

Further, in the extrusion process, means, not illustrated in FIGURES 3and 4 may desirably be provided for centering the pressure member 8, orthe dummy block 9 of it, within the container in order to guide the saidterminal part relatively to the case 1 and encased billet 2, and ensurethat pressure is applied to the latter rather than the former. Suchguide means may assume the form of a centering ring surrounding thepressure member and slidable with respect to it or/and to the container.

Various other modifications may be made in the structural detailsillustrated and described, and the invention may be applied forhot-working processes as well as to materials other than thosespecifically mentioned.

While I have shown and described preferred embodiments of my invention,it may be otherwise embodied within the scope of the appendant claims.

What I claim is:

1. A method of hot piercing material selected from the group consistingof steels, alloy steels, refractory alloys and cermets, which comprisesencasing a billet of said material in a sheath so that there is aclearance space between said billet and said sheath, said sheath beingmade of a rigid material, interposing in said clearance space asubstance selected from within the group of substances having asubstantial viscosity in the range of temperatures including the desiredhot piercing temperature of said billet, heating said billet, saidsheath and said substance to a desired hot piercing temperature of saidbillet, placing said heated billet and its sheath into a press chamberof a piercing press having a piercing nose of a desired piercingdiameter adapted to engage I locally said billet at one end thereof, andpiercing said billet by application of piercing pressure by said nosedirectly to said billet but not to said sheath thereby causing saidmaterial of said billet to flow rearwardly in said References CitedUNITED STATES PATENTS 2,756,494 7/ 1956 Sejournet 72-42 2,810,478 10/1957 Sejournet 724-2 3,072,251 l/ 1963 Sauve 7242 3,254,401 6/ 1966Dalton 72-42 OTHER REFERENCES Paret: Stainless-Steel Extrusions, p. 116, Machine Design, vol. 31, No. 1, Jan. 8, 1959, pub. by Penton Pub.00., Cleveland, Ohio.

CHARLES W. LANHAM, Primary Examiner.

20 K. C. DECKER, Assistant Examiner.

1. A METHOD OF HOT PIERCING MATERIAL SELECTED FROM THE GROUP CONSISTINGOF STEELS, ALLOY STEELS, REFRACTORY ALLOYS AND CERMETS, WHICH COMPRISESENCASING A BILLET OF SAID MATERIAL IN A SHEATH SO THAT THERE IS ACLEARANCE SPACE BETWEEN SAID BILLET AND SAID SHEATH, SAID SHEATH BEINGMADE OF A RIGID MATERIAL, INTERPOSING IN SAID CLEARANCE SPACE ASUBSTANCE SELECTED FROM WITHIN THE GROUP OF SUBSTANCES HAVING ASUBSTANTIAL VISCOSITY IN THE RANGE OF TEMPERATURES INCLUDING THE DESIREDHOT PIERCING TEMPERATURE OF SAID BILLET, HEATING SAID BILLET, SAIDSHEATH AND SAID SUBSTANCE TO A DESIRED HOT PIERCING TEMPERATURE OF SAIDBILLET, PLACING SAID HEATED BILLET AND ITS SHEATH INTO